Catheter for the delivery of a therapeutically active substance

ABSTRACT

The invention features a catheter particularly for the delivery of a therapeutically active substance comprising a catheter body and an inflatable structure comprising three inflatable elements and a diaphragm fixed to these elements and defining with them, a passage duct for the body fluid and a sealed cavity to contain a therapeutically active substance. The said first (3), second (4) and third (7) inflatable elements are made of one preformed piece consisting of a helically coiled tube, said third element (7) being constituted by one or more turns of the coil, the diameter of the said tube at the portion constituting the third element being less than the diameter of the said tube at the tube portions constituting the said first and second elements respectively and intended to rest against the internal wall of said body duct; the said catheter body is disposed inside the coil of the said tube, in the aforementioned duct. This invention is useful in the preventive treatment of restenosis.

FIELD OF THE INVENTION

The subject of the present invention is a catheter intended to beintroduced into a bodily canal in which a fluid flows, particularly inorder to deliver thereto a therapeutically active substance in alocalised region of said canal, without interrupting the flow of saidfluid.

The main application of the invention is in the field of treating bloodvessels and, even more particularly, in the treatment of restenosis.

The catheter according to the present invention may, however, be usedfor treating a variety of disorders of various morphological canals inthe human or animal body, such as, in particular, the urinary canalsand, in particular, the urethra, or else the digestive canals and, inparticular, the oesophagus.

This catheter is mainly intended for locally delivering atherapeutically active substance, but also enables isolating a segmentof the wall of a bodily canal, for example for assisting a surgicaloperation upon said wall segment thus isolated.

In order to clarify the explanation, the catheter according to thepresent invention will be described in its preferred particularapplication to the preventive treatment of restenosis.

BACKGROUND OF THE INVENTION

It is known that restenosis can be defined as a recurrent reduction inthe calibre of the coronary lumen at the site initially expanded withsuccess during a coronary transluminal angioplasty.

This disorder remains the main current limitation on balloon coronaryangioplasty since it leads to a new angioplasty in approximately 15 to30% of cases within the 6 months following a successful angioplasty.

Various solutions have been envisaged to date for the prevention ofrestenosis, and these have led to more or less satisfactory results.

Thus, the use of so-called "ablative" angioplasty techniques such as,for example, laser angioplasty or atherectomy have not permitted asignificant reduction in the incidence of restenosis.

In contrast, fitting a coronary endoprosthesis after angioplastyconstitutes a relatively effective treatment in the prevention ofrestenosis, since it leads to a reduction by approximately 30% in therisk of restenosis.

However, the systematic fitting of endoprostheses cannot be envisaged,insofar as this could lead to operating unnecessarily on a large numberof patients who would have suffered no restenosis without anendoprosthesis, and insofar as there would still be a relatively largenumber of patients suffering restenosis in spite of the fitting of anendoprosthesis.

Systemic administration of pharmacologically active substances such asantithrombins, converting enzyme inhibitors, some vasodilators or somehypolipidemic agents has to date not led to entirely satisfactoryresults.

This is why the use of devices intended for local delivery oftherapeutically active substances constitutes a more promising prospectin the prevention of restenosis.

In fact, this method makes it possible to administer, at the dilatedsite, products which are specifically targeted against the mechanisms ofrestenosis, including products which are toxic for the rest of the body,in predetermined concentrations and over a variable period of time.

In order to be usable in the context of this method, the device mustpermit local delivery of the active substance without interruption tothe flow of fluid in the bodily canal.

A catheter satisfying this requirement has been proposed in the documentEP 0.526.102.

This catheter is generally composed of an elongate tubular elementincluding an inflatable structure arranged at its distal part.

This inflatable structure consists of a set of identical toric balloonsand a membrane fixed to these balloons, this structure being designed insuch a way that, when it is inflated, it defines:

on the one hand, a central passage channel for the bodily fluid; and

on the other hand, a substantially leaktight cavity or pouch, intendedto contain said therapeutically active substance and defined by theballoons, by the outer surface of the membrane and by the inner surfaceof the bodily canal.

The catheter body includes a first internal channel which communicates,on the one hand, with the balloons and, on the other hand, with a meansmaking it possible to inflate and deflate these balloons; and a secondinternal channel which communicates, on the one hand, with theaforementioned cavity and, on the other hand, with a supply source offluid containing a pharmacologically active substance.

As can be seen in the aforementioned document, in the diagramsillustrating the various embodiments of this catheter, the catheter bodyas well as the various intermediate balloons intended for holding themembrane in position are in direct contact with the bodily canal.

The result of this is that such a device does not make it possible totreat effectively, that is to say in a single operation, the entiresurface of the bodily canal at the dilated site, since the activesubstance cannot reach the portion of the surface of the bodily canalwhich is in contact with the balloons and the catheter body, unless theinflatable structure is displaced, and this complicates the operation.

SUMMARY OF THE INVENTION

The object of the present invention is to solve this technical problemby providing a novel design of catheter which is simpler to produce andfit, and which makes it possible to deliver a therapeutically activesubstance in a single operation over the entire surface of the bodilycanal to be treated.

The solution according to the present invention, for solving thistechnical problem, consists of a catheter intended to be introduced intoa bodily canal in which a fluid flows, particularly in order to deliverthereto, in a localised region, a therapeutically active substancecarried by a second fluid, of the type comprising:

a catheter body including an elongate tubular element having a proximalpart and a distal part;

an inflatable structure, arranged at the distal part of said catheterbody and including:

a first inflatable element and a second inflatable element which, wheninflated:

are axially separated from one another;

each bear in leaktight fashion against the internal wall of the saidbodily canal; and

each has a substantially central opening;

a membrane, fixed to said first and second inflatable elements anddefining with them, when they are inflated;

on the one hand, a substantially cylindrical sleeve, joining togetherthe central openings of the said first and second inflatable elements,in leaktight fashion, thus forming a channel for passage of the bodilyfluid; and

on the other hand, a substantially leaktight cavity, capable ofcontaining said therapeutically active substance and defined by saidfirst and second inflatable elements, by the external surface of saidmembrane and by the internal surface of the bodily canal;

a third inflatable element, arranged between said first and secondinflatable elements, designed to keep said membrane in position when itis inflated;

said catheter body including a first internal channel whichcommunicates, on the one hand, with said first, second and thirdinflatable elements and, on the other hand, with a means making itpossible to inflate and deflate these elements; and a second internalchannel which communicates on the one hand, with the aforementionedcavity and, on the other hand, with a supply source of fluid containingsaid pharmacologically active substance, and optionally a third internalchannel, independent from said second internal channel, whichcommunicates on the one hand with the aforementioned cavity, and on theother hand, with a supply source of fluid optionally containing atherapeutically active substance, or with a suction device,characterised in that said first, second and third inflatable elementsare made in a single preformed part, consisting of a helically woundtube, said third element consisting of one or more turns of thiswinding, the diameter of said tube at the portion constituting saidthird element being less than the diameter of said tube at the tubeportions which respectively constitute said first and second elementsand are intended to bear against the internal wall of said bodily canal;and characterised in that said catheter body is arranged inside thewinding of said tube, in the aforementioned central channel.

Thus, as will be understood, the originality of the present inventionresides in the fact that neither the catheter body nor the thirdinflatable element intended to hold the membrane in position aredirectly in contact with the internal surface of the morphologicalcanal, which makes it possible to treat, in a single operation, all ofthe surface of the bodily canal at the site which is chosen.

This object is achieved, on the one hand, insofar as the inflatablestructure surrounds the catheter body, such that the latter is not incontact with the bodily canal and, on the other hand, insofar as thetube constituting the inflatable structure has a variable diameter, thetube portions defining the cavity intended to contain the activesubstance having a larger diameter than that of the intermediate tubeportion constituting the part intended to hold the membrane, such thatthe latter portion of the tube is not in contact with the bodily canal.

According to another particular feature of the invention, the tubeportion respectively constituting the first and second inflatableelements has a variable-pitch helix configuration defining a firstregion, consisting of at least two contiguous turns which are intendedto bear in leaktight fashion against the internal wall of the bodilycanal, and a second region, extending the first and extending as far asthe catheter body, said second region forming at least one helix portionwhose pitch is greater than that of the helix formed by the turns in thefirst region, the diameter of the tube in the second region beingpreferably less than the diameter of the tube in the first region.

This design of the first and second inflatable elements is particularlyadvantageous since it makes non-traumatic the progress of the catheterwhen it enters the bodily canal, and, above all, when it is withdrawntherefrom.

In order to facilitate the folding and refolding of the inflatablestructure around the catheter body and thus make the latter easier toinsert and withdraw, the inflatable structure is preformed, preferablyso as to have, seen in cross section relative to the catheter body, thegeneral shape of a spiral which is closed on itself by a series of atleast two alternate loops.

According to another particular feature of the invention, in order tofurther facilitate the refolding after an operation, the aforementionedcatheter is provided with means for assisting refolding of theaforementioned inflatable structure after deflation.

According to a first embodiment, these means comprise two elasticthreads arranged respectively around the first and second inflatableelements while being connected thereto preferably along a generatrix.

According to another embodiment, these means comprise two substantiallycylindrical elastic membranes respectively enclosing the first andsecond inflatable elements while being connected thereto preferablyalong a generatrix.

The design of the inflatable structure, combined with the aforementionedmeans for assisting refolding, guarantees the safety of the catheteraccording to the invention when it is introduced into the bodily canaland withdrawn therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood, and other objects, features andadvantages thereof will emerge more clearly on reading the followingexplanatory description, made with reference to the appended schematicdrawings which are given solely by way of non-limiting example andillustrate a currently preferred embodiment of the invention, and inwhich:

FIG. 1 is a longitudinal schematic view showing the distal end of acatheter according to a currently preferred embodiment of the invention,represented when it is inflated in a bodily canal;

FIG. 2A is a view in cross section along the line IIA--IIA in FIG. 1;

FIG. 2B is a view in cross section along the line IIB--IIB in FIG. 1;

FIG. 2C is a view in cross section along the line IIC--IIC in FIG. 1;

FIG. 3 is a view in longitudinal section illustrating the distal end ofa catheter according to another particular embodiment of the invention,including means for assisting refolding of the inflatable structure,which is represented in the inflated state;

FIG. 4 is a similar view to FIG. 3, of the same catheter includingdifferent means for assisting refolding of the inflatable structure;

FIG. 5 is a schematic view in cross section of a catheter according tothe present invention, provided with means for assisting refolding andrepresented in the inflated state;

FIG. 6 is a view in cross section of the same catheter, the inflatablestructure being in the deflated and refolded state

FIG. 7 is a longitudinal schematic view showing the distal end of acatheter according to another embodiment of the invention, which has asecond and third internal channel;

FIG. 7A is a view in cross-section along the line A--A in FIG. 7; and

FIG. 8 is a partial view of the catheter body according to view F inFIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

Thus, FIG. 1 represents the distal end of a catheter equipped with aninflatable structure according to a currently preferred embodiment ofthe invention, when it is inflated in a bodily canal such as, forexample, a blood vessel denoted by the reference number 1.

A catheter according to the present invention essentially comprises acatheter body including an elongate tubular element which has a proximalpart and a distal part, as well as an inflatable structure generallydenoted by the reference number 2, arranged at the distal part of thecatheter body.

Only the catheter body part bearing the inflatable structure isrepresented in FIG. 1.

The proximal part (not represented and denoted by the letter P) of thecatheter is located on the left in FIG. 1, while the distal part (notrepresented and denoted by the letter D) is located on the right.

The inflatable structure 2 generally comprises a preformed tube ofvariable diameter, having a helicoid turn configuration defining threeregions respectively designated by "first", "second" and "third"inflatable element, as well as a membrane fixed to this tube.

In the inflated state, represented in FIG. 1, the first inflatableelement 3 and the second inflatable element 4 are axially separated fromeach other, each bearing in leaktight fashion against the internal wallof the bodily canal 1 and each having a substantially central opening21.

As can be seen, the tube portion respectively constituting the first andsecond inflatable elements 3, 4 generally has a variable-pitch helixconfiguration defining a first region, consisting of at least twocontiguous turns which are intended to bear in leaktight fashion, in theinflated state, against the internal wall 5 of the bodily canal 1, and asecond region, extending the first and continuing as far as the catheterbody 6, said second region forming at least one helix portion, the pitchof which is greater than that of the helix formed by said turns in thefirst region, the diameter of the tube in the second region beingpreferably less than the diameter of the tube in the first region.

The number of contiguous turns constituting the first region of thefirst and second inflatable elements 3, 4 may vary from 2 to severaltens, depending in particular on the calibre of the bodily canal and thetreatment to be carried out.

By way of example, the first region of the first and second inflatableelement 3, 4 may comprise four contiguous turns, respectively denoted bythe reference numbers 31 and 41.

The distance between the group of proximal contiguous turns 31 and thegroup of distal contiguous turns 41 can vary within wide limits, forexample between 5 mm and 100 mm.

This distance will be approximately 10 mm in the case of a preventivetreatment for restenosis.

The second region of the first and second inflatable elements 3, 4,respectively represented by the reference numbers 32 and 42, forms atleast one helix portion whose pitch is greater than that of the helixformed in the first region. This region will generally formsubstantially one turn.

The tube portions forming the second regions 32 and 42 each extend asfar as the catheter body while preferably giving the inflatablestructure 2, when seen in cross section, the general shape of atrapezium whose long base lies level with the catheter.

The tube portions 32 and 42 advantageously have a smaller diameter thanthe tube portions defining the contiguous turns 31 and 41.

By way of example, the diameter of the tube at the portions 32 and 42may be of the order of 0.5 mm and the diameter of the tube at thecontiguous turns 31 and 41 may be of the order of 0.7 mm.

The tube portion defining the third inflatable element 7 which joinstogether the groups of turns 31 and 41 also has a helix configurationand may comprise one or more turns, depending on the distance separatingthe groups of turns 31 and 41.

The diameter of the tube portion defining the third inflatable element 7is less than the diameter of the tube at the turns 31 and 41.

By way of example, the diameter of the tube at the inflatable element 7may be of the order of 0.5 mm when the diameter of the tube at the turns31 and 41 is of the order of 0.7 mm.

This results, in particular, in the third inflatable element 7 not beingdirectly in contact with the internal surface 5 of the bodily canal 1,as can be seen in FIG. 1, which constitutes one of the original featuresof the catheter according to the invention.

The pitch of the helix at the third element 7 will advantageously begreater than that of the helix formed by the groups of turns 31 and 41.

However, this is no more than a preferred embodiment, it being possiblefor the turns constituting the third inflatable element to be alsocontiguous with each other and optionally with the turns 31 and 41 ofthe first and second inflatable elements.

The tube forming the first, second and third inflatable elements mayadvantageously be made of a thermoplastic such as, for example, apolyamide, an optionally cross-linked polyethylene, a polyurethane or apolyethylene terephthalate.

This tube may be formed from a tube having a constant diameter which isfirstly expanded zonally so as to obtain the desired diameters in eachof the portions corresponding to the first, second and third inflatableelements.

The tube thus obtained is secondly shaped under pressure so as to obtainthe desired final profile (helicoid turns).

The aforementioned design makes it possible to avoid the possibleappearance of creases on the turns during inflation. Such creases wouldin fact impair correct deployment of the inflatable structure 2 and theleaktightness of the cavity 9 at the contiguous turns 31 and 41 of thefirst and second inflatable elements 3, 4.

The inflatable structure 2 also comprises a membrane 8 which is fixed tothe first and second inflatable elements 3, 4 while thus defining withthem, when they are inflated:

on the one hand, a substantially cylindrical sleeve joining together inleaktight fashion the central openings 21 of said first and secondinflatable elements 3, 4 while thus forming a channel for passage of thebodily fluid; and

on the other hand, a substantially annular and leaktight cavity 9,intended to contain one or more therapeutically active substances andlaterally bounded, on the proximal side, by the most distal turn of thefirst inflatable element 3, and on the distal side, by the most proximalturn of the inflatable element 4, and, radially, externally by theinternal wall 5 of the bodily canal 1 and internally by the externalsurface of the membrane 8.

Within the context of the present description and claims,"therapeutically active substance" is understood as meaning anysubstance or composition having a therapeutic activity. Such a substancecan be in various forms such as, for example, a glue, a gel,microspheres, particles or nanoparticles.

The membrane 8 is preferably arranged at the level of the internaldiameter of the contiguous turns 31 and 41 of the first and secondinflatable elements 3, 4 while being connected thereto preferablyirreversibly, for example by adhesive bonding, thermally activatedadhesive bonding, welding or dip-coating.

As will be understood, the membrane portion contained between the twogroups of contiguous turns 31 and 41 thus defines a tube which is openat its two ends, creating a passage for the flow of the bodily fluid inthe direction represented by the arrow F.

By construction, this passage channel for the bodily fluid may have arelatively large diameter, allowing the catheter to be fitted withoutinterrupting the flow of this fluid.

By way of example, the diameter of this channel may be 2.5 mm, in thecase of a 3.5 mm artery, which makes it possible to obtain a flow rateof the bodily fluid through the catheter which is greater than 50% ofthe normal flow rate in the absence of a catheter.

When the tube forming the first, second and third inflatable elements 3,4, 7 is inflated, the inflatable structure 1 will be deployed and inducea tension on the membrane.

The membrane 8 is generally designed in such a way that the centralchannel is cylindrical when this membrane is under tension after thefirst, second and third inflatable elements 3, 4, 7 have been inflatedto a predetermined pressure (generally of the order of 6 bar).

The membrane will preferably have a radially elastic behaviour, in orderto follow the compliance of the contiguous turns 31, 41.

To this end, the membrane may be made of a material such as a silicone,a polyurethane or a polyamide which can withstand radial stretching.

In a currently preferred embodiment, the membrane is made ofpolyurethane and can withstand radial stretching equivalent to two timesits initial diameter.

The membrane 8 is deployed and shaped under the effect of the inflationof the first, second and third inflatable elements 3, 4, 7, by thuschanging from a relatively flexible state to a semi-rigid state,creating a barrier between the tubular passage for the bodily fluid andthe aforementioned annular space 9, this space being relativelyleaktight with respect to the surrounding medium and being thus capableof serving as a diffusion cavity or pouch for the therapeutically activesubstance(s) used.

In the embodiment represented in FIGS. 3 and 4, the inflatable structure2 includes a second membrane 28, arranged radially and externallyrelative to the first membrane 8, for enclosing the first and secondinflatable elements 3, 4.

The second membrane 28 may optionally be extended as far as the catheterbody, in order to enclose the latter partially, as represented in FIGS.3 and 4.

The second membrane will be connected, for example by adhesive bonding,thermally activated adhesive bonding, welding or dip-coating, to thefirst and second inflatable elements 3, 4 and, optionally, to thecatheter body as well as the first membrane 8.

This particular design makes it possible to obtain better leaktightnessof the annular cavity 9 as well as better longitudinal and transversestrength of the inflatable structure 2.

It should further be noted that the first membrane 8 is also fixed, forexample by adhesive bonding, thermally activated adhesive bonding,welding or dip-coating, to the third inflatable element 7, the lattercontributing to keeping the membrane under tension when the inflatablestructure 2 is inflated, in particular preventing the first and secondinflatable elements 3 and 4 from moving towards each other.

The role of the third inflatable element is essential for keeping thecross section of the passage channel for the bodily fluid constantduring the operation, regardless of the distance separating the firstand second inflatable elements 3, 4.

The catheter according to the present invention includes a catheterbody, generally consisting of a flexible elongate tubular element, thetotal length of which may be approximately 135 cm and the diametervariable from 0.70 mm to 3 mm, depending on the desired application.

This diameter will advantageously be approximately 1 mm in the case ofthe preventive treatment of restenosis.

The catheter body preferably consists of a plurality of parts, withdifferent diameters, made of materials which have differentflexibilities.

The proximal part has a total length of approximately 110 cm and thedistal part has a total length of approximately 25 cm.

The distal end, represented in FIG. 1 and intended to support theinflatable structure, is advantageously stretched over a length slightlygreater than the length of the portion of the bodily canal to betreated, for example by approximately 3 cm in this particular case.

The catheter body may be made, for example, of a material such as asemi-rigid thermoplastic like, for example, a high-density polyethylene,a polyamide, or a copolymer of the type PEBAX® marketed by the companyATOCHEM.

The catheter body, and this constitutes an original feature of theinvention, is arranged inside the aforementioned inflatable structure,that is to say inside the passage channel for the bodily fluid, as shownin particular by FIG. 2B and 2C.

This has the particular result that the catheter body is not in directcontact with the internal wall 5 of the bodily canal 1, in particular atthe site to be treated, which constitutes a determining advantage overthe state of the art catheter described in document EP-0.526.102. 12

According to the invention, the catheter body includes a first internalchannel 11 which communicates, on the one hand, with the tubeconstituting the first, second and third inflatable elements 3, 4, 7and, on the other hand, with a means (not represented) making itpossible to inflate and deflate this tube.

In the currently preferred embodiment, the internal channel 11 and thetube constituting the first, second and third inflatable elements 3, 4and 7 communicate via the tube portion 32 defined above.

The catheter body further comprises a second internal channel 12 whichcommunicates, on the one hand, with the aforementioned annular cavity 9,and on the other hand, with a supply source of fluid containing one ormore pharmacologically active substances.

In the currently preferred embodiment, the second internal channel 12 ofthe catheter body and the aforementioned cavity 9 communicate throughone or more diffusion orifices 13 made in the catheter body and in themembrane 8, preferably in the form of notches extending longitudinallyand having a length of approximately 2 mm.

In the embodiment represented in FIG. 1, there is only one singlediffusion orifice 13, made in the form of a notch with a length of 2 mmand having a diameter of 0.2 mm.

The particular form of this notch allows uniform diffusion of thepharmacologically active substance in the annular cavity 9.

It should be noted that, by virtue of this particular form, thepharmacologically active substance diffuses through the orifices 13 inthe form of drops which are non-traumatising for the wall of themorphological canal, which also constitutes an advantage.

The wall of the canal is therefore progressively affected by thepharmacologically active substance, it being possible for the diffusionrate and therefore the pressure inside the annular cavity 9 to besubsequently increased substantially, if necessary.

According to a particular feature, the external surface of the secondmembrane 28 may be porous in the part contained between the first andsecond inflatable elements 3, 4, allowing even more uniform and evenless traumatising diffusion of the pharmacologically active substanceinside the annular cavity 9.

The catheter body may further comprise a third internal channel 12A,which is independent from the second internal channel 12, and whichcommunicates on the one hand with the aforementioned annular cavity 9,and on the other hand, either with a supply source of fluid optionallycontaining one or more active substances identical or different to theactive substance(s) which can be carried by the second internal channel12, or with a suction device.

In the currently preferred embodiment, represented in FIGS. 7, 7A and 8,the communication between the third internal channel 12A of the catheterbody and the aforementioned cavity 9 is made via one or more diffusionorifices 13A which preferably have the same conformation as theaforementioned diffusion orifices 13.

The suction device connected to the eventual third internal channel 12Amay serve, in the context of the treatment of aneurysms for example, toallow evacuation of the liquid contained in the aneurysm pouch, and inthis case, the second internal channel 12 allows filling said aneurysmpouch by means of an adequate therapeutically active substance.

The catheter body may further comprise a fourth internal channel 14,constituting a passageway for a guide wire (not represented) or anyother probe.

The catheter used in the context of the present invention may be of the"quick change" type, that is to say that the guide wire will passthrough its body only over a small portion of its length, correspondingsubstantially to the distal part. In this case, in the proximal part,the catheter body may include only the first and second aforementionedinternal channels.

The catheter may also be of a type known by the term "over the wire",that is to say that the guide will pass through the body over its entirelength. In this case, it will be necessary to provide the aforementionedthird channel, constituting the passageway for the guide.

The catheter may also be further provided with a core with a highelastic modulus, such as defined in the document WO 95/28197, extendingalong the catheter body substantially as far as the distal end, in orderto allow optimum transmission of the thrust exerted by the doctor on theproximal end of the catheter when it is introduced into the bodilycanal.

In order to allow the catheter according to the present invention to beintroduced into and withdrawn from a bodily canal, it is necessary forthe catheter body to have, in particular at the distal part bearing theaforementioned inflatable structure, a reduced diameter when the latteris deflated.

In order to facilitate folding of the inflatable structure about thecatheter body and thus to make the latter easier to introduce into thebodily canal the inflatable structure is preformed, for example with thestructure represented in FIG. 6, this preforming further giving theinflatable structure a "memory" facilitating its refolding and thusmaking it easier to withdraw the catheter after the operation.

As shown by FIG. 6, the inflatable structure can thus be formed, forexample under pressure, in order to have, seen in cross section relativeto the catheter body, the general shape of a turn which is closed onitself by two alternate loops 16, 17.

In order to further facilitate the refolding of the inflatable structure2, a catheter according to the invention may further be provided withmeans for assisting refolding of the aforementioned inflatable structureafter it is deflated.

According to a first embodiment, represented in FIG. 3, these means forassisting refolding comprise two elastic threads 18, 19, arrangedrespectively around the first and second inflatable elements 3, 4, whilebeing connected thereto preferably along a generatrix 20 (see FIG. 5).

This connection may be made, for example, by adhesive bonding, thermallyactivated adhesive bonding, welding or dip-coating.

The aforementioned elastic elements may be made of a highly elasticmaterial such as, for example, latex or some polyurethanes or silicones.

According to another embodiment, represented in FIG. 4, the means forassisting refolding comprise two substantially cylindrical elasticmembranes 23, 24, respectively enclosing the first and second inflatableelements 3, 4, being also connected thereto preferably along ageneratrix 20 (see FIG. 5).

As will be understood, the elements for assisting refolding will act,after the inflatable structure 2 is deflated, by exerting an elasticreturn force which facilitates the refolding of this structure 2 intoits initial position, as represented in FIG. 6.

This particular feature gives the catheter of the invention greatersafety when it is introduced into and withdrawn from the bodily canal.

The way in which the catheter according to the invention is used can bededuced easily from its structure which has just been described.

Before the catheter is introduced into the bodily canal, the channel 12of the catheter is filled with a physiological saline solution in orderto remove all the air bubbles present in this channel.

The catheter, provided with its inflatable structure in the deflatedstate, and refolded, is introduced in the traditional way, for exampleusing a guide wire, into a morphological canal such as a blood vesseland is positioned using radio-opaque markers 10 (see FIG. 1) at thelocation of the site intended to be treated, for example the site of astenosis dilated by angioplasty.

When the catheter is positioned in this way, the inflatable structure 2is supplied through the inflation conduit 11 up to a pressure equal toapproximately a fraction of the normal working pressure (approximately 2bar).

During this preliminary inflation, the inflatable structure 2 will bedeployed and will cause the membrane 8 to be tensioned.

The annular cavity 9 is then supplied, via the channel 12, with a smallquantity (of the order of 1 cm³) of a fluid containing one or moreactive substances in order to replace the physiological saline solutionpresent in said channel. The maximum pressure during this operation is 1bar.

The inflatable structure is then brought progressively to the desiredsealing pressure which may be of the order of 4 to 14 bar.

The therapeutically active substance is then introduced into theleaktight annular cavity 9 at the desired rate.

A number of therapeutically active substances may be administered in thecontext of the present invention, such as, for example, antithrombins,converting enzyme inhibitors, vasodilators, lipidemic agents or evensome proto-oncogenes.

The catheter which has just been described is particularly advantageoussince it permits very accurate diffusion of the various therapeuticallyactive substances at desired concentrations for a predetermined lengthof time.

In addition, the particular design of this catheter allows all of thesurface of the bodily canal to be treated in a single operation at thechosen site.

The catheter which has just been described may also be used to isolate asegment of the wall of a bodily canal, especially for treating ananeurysm, for assisting a surgical operation upon said wall segment thusisolated, such as, for example a by-pass, or even for performing aselective embolisation.

In the particular case of the treatment of aneurysms, the catheteraccording to the present invention enables isolating the malformation ofthe rest of the blood flow, so as to be able to treat the blood flowmore effectively and more safely than by existing means. The risk ofaccidental embolisation is thus considerably reduced.

We claim:
 1. A catheter for introduction into a bodily canal in which afluid flows, in order to deliver thereto, in a localised region, atherapeutically active substance carried by a second fluid, of the typecomprising:a catheter body including an elongate tubular element havinga proximal part and a distal part; an inflatable structure, arranged atthe distal part of said catheter body and including:a first inflatableelement and a second inflatable element which, when inflated:are axiallyseparated from one another; each bear in leaktight fashion against theinternal wall of said bodily canal; and each has a substantially centralopening; a membrane, fixed to said first and second inflatable elementsand defining with them, when they are inflated:a substantiallycylindrical sleeve, joining together the central openings of said firstand second inflatable elements, in leaktight fashion, thus forming achannel for passage of the bodily fluid; and a substantially leaktightcavity, capable of containing said therapeutically active substance anddefined by said first and second inflatable elements, by the externalsurface of said membrane and by the internal surface of the bodilycanal; a third inflatable element, arranged between said first andsecond inflatable elements, designed to keep said membrane in positionwhen it is inflated;said catheter body including a first internalchannel which communicates with said first, second and third inflatableelements and has a means for inflating and deflating said elements; asecond internal channel which communicates with said cavity and with asupply source of fluid containing said pharmacologically activesubstance, wherein said first, second and third inflatable elements aremade in a single preformed part, consisting of a helically wound tube,said third element consisting of at least one turn of said helicallywound tube, the diameter of said tube at the portion constituting saidthird element being less than the diameter of said tube at the tubeportions which respectively constitute said first and second elementsand are intended to bear against the internal wall of said bodily canal;and wherein said catheter body is arranged inside the winding of saidhelically wound tube.
 2. The catheter as claimed in claim 1, wherein thetube portion respectively constituting the first and second inflatableelements has a variable-pitch helix configuration defining a firstregion, consisting of at least two contiguous turns which are adopted tobear in leaktight fashion against the internal wall of the bodily canal,and a second region, extending the first and continuing as far as thecatheter body, said second region forming at least one helix portionwhose pitch is greater than that of the helix formed by the turns in thefirst region.
 3. The catheter as claimed in claim 2, wherein thediameter of the tube in said second region is less than the diameter ofthe tube in said first region.
 4. The catheter as claimed in claim 1,wherein said inflatable structure is preformed.
 5. The catheter asclaimed in claim 1, wherein said inflatable structure is preformed so asto have, seen in cross section relative to the catheter body, thegeneral shape of a spiral which is closed on itself by a series of atleast two alternate loops.
 6. The catheter as claimed in claim 1, whichcomprises means for assisting refolding of said inflatable structureafter deflation.
 7. The catheter as claimed in claim 6, wherein saidmeans for assisting refolding comprise two elastic threads arrangedrespectively around the first and second inflatable elements while beingconnected thereto.
 8. The catheter as claimed in claim 6, wherein saidmeans for assisting refolding comprise two elastic threads arrangedrespectively around the first and second inflatable elements while beingconnected thereto along a generatrix.
 9. The catheter as claimed inclaim 6, wherein said means for assisting refolding comprise twosubstantially cylindrical elastic membranes respectively enclosing thefirst and second inflatable elements while being connected thereto. 10.The catheter as claimed in claim 6, wherein said means for assistingrefolding comprise two substantially cylindrical elastic membranesrespectively enclosing the first and second inflatable elements whilebeing connected thereto along a generatrix.
 11. The catheter as claimedin claim 1, wherein said membrane is arranged at the level of theinternal diameter of the contiguous turns of the first and secondinflatable elements while being connected thereto.
 12. The catheter asclaimed in claim 1, wherein said membrane is arranged at the level ofthe internal diameter of the contiguous turns of the first and secondinflatable elements while being connected thereto irreversibly by ameans selected from the group consisting of adhesive bonding, thermallyactivated adhesive bonding, welding, and dip-coating.
 13. The catheteras claimed in claim 11, wherein said membrane is made of a materialwhich can withstand radial stretching.
 14. The catheter as claimed inclaim 13, wherein said material which can withstand radial stretching isselected from the group consisting of silicone, polyurethane, andpolyamide.
 15. The catheter as claimed in claim 1, wherein saidinflatable structure includes a second membrane, arranged radially andexternally relative to the first membrane and enclosing said first andsecond inflatable elements.
 16. The catheter as claimed in claim 1,wherein said second internal channel of the catheter body and saidcavity communicate via at least one diffusion orifice which are in theform of longitudinal notches which diffuse the therapeutically activesubstance in the form of drops which are non-traumatising for the wallof the bodily canal.
 17. The catheter as claimed in claim 1, whereinsaid catheter body includes a third internal channel, independent fromsaid second internal channel, which communicates with said cavity, andwith a supply source of fluid.
 18. The catheter as claimed in claim 1,wherein said catheter body includes a third internal channel,independent from said second internal channel, which communicates withsaid cavity, and with a supply source of fluid containing atherapeutically active substance.
 19. The catheter as claimed in claim1, wherein said catheter body includes a third internal channel,independent from said second internal channel, which communicates withsaid cavity, and with a suction device.